Chapter 8- Lecture Outline Flashcards
The Energy of Life
The living cell is a miniature chemical factory where thousands of reactions occur
The cell extracts energy stored in sugars and other fuels and applies energy to perform work
Some organisms even convert energy to light, as in bioluminescence
_______________ is the totality of an organism’s chemical reactions
Metabolism is an emergent property of life that arises from orderly interactions between molecules
Organization of the Chemistry of Life into Metabolic Pathways
Metabolism
A metabolic pathway begins with a specific molecule and ends with a product
Each step is catalyzed by a specific enzyme
______________________ release energy by breaking down complex molecules into simpler compounds
Catabolic pathways
________________________ the breakdown of glucose
in the presence of oxygen, is an example of a pathway of catabolism
Cellular respiration,
_____________ consume energy to build complex molecules from simpler ones
The synthesis of protein from amino acids is an example of anabolism
Anabolic pathways
__________ is the study of how energy flows through living organisms
Forms of Energy
Bioenergetics
__________s the capacity to cause change
Energy exists in various forms, some of which can perform work
Energy
__________________ is energy associated with motion
__________________: is kinetic energy associated with random movement of atoms or molecules
__________________ is energy that matter possesses because of its location or structure
______________ is potential energy available
for release in a chemical reaction
Kinetic energy
Heat (thermal energy)
Potential energy
Chemical energy
Energy can be converted from one form to another
but it can be neither created nor destroyed
___________________
According to the first law of thermodynamics, the energy of the universe is constant
Energy can be transferred and transformed,
but it cannot be created or destroyed
The first law is also called the principle of conservation of energy
Figure 8.3
The First Law of Thermodynamics
___________________
During every energy transfer or transformation, some energy is unusable, and is often lost
as heat
According to the second law of thermodynamics
Every energy transfer or transformation increases the entropy
The Second Law of Thermodynamics
occur without energy input; they can happen quickly or slowly
For a process to occur without energy input,
it must increase the entropy of the universe
Spontaneous processes
Cells create ordered structures from less ordered materials
Organisms also replace ordered forms of matter and energy with less ordered forms
Energy flows into an ecosystem in the form of light and exits in the form of heat
The evolution of more complex organisms does not violate the second law of thermodynamics
Entropy (disorder) may decrease in an organism, but the universe’s total entropy increases
Biologists want to know which reactions occur spontaneously and which require input of energy
To do so, they need to determine energy changes that occur in chemical reactions
Free-Energy Change, G
A living system’s free energy is energy that can do work when temperature and pressure are uniform, as in a living cell
free energy
The change in free energy (∆G) during a process is related to the change in enthalpy, or change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin units (T)
∆G = ∆H - T∆S
Only processes with a negative ∆G are spontaneous
Spontaneous processes can be harnessed to perform work
Free Energy, Stability, and Equilibrium
Free energy is a measure of a system’s instability, its tendency to change to a more stable state
During a spontaneous change, free energy decreases and the stability of a system increases
Equilibrium is a state of maximum stability
A process is spontaneous and can perform work only when it is moving toward equilibrium
Free Energy and Metabolism
The concept of free energy can be applied to the
chemistry of life’s processes
___________ proceeds with a net release of free energy and is spontaneous
____________________ absorbs free energy from its surroundings and is nonspontaneous
An exergonic reaction
An endergonic reaction
A cell does three main kinds of work
Chemical
Transport
Mechanical
To do work, cells manage energy resources by __________________ the use of an exergonic process to drive an endergonic one
energy coupling,
ATP (adenosine triphosphate) is the cell’s energy shuttle
ATP is composed of ribose (a sugar), adenine
(a nitrogenous base), and three phosphate groups
The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis
Energy is released from ATP when the terminal phosphate bond is broken
This release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves
How the Hydrolysis of ATP Performs Work
The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP
In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction
The reactant that an enzyme acts on is called
the enzyme’s substrate
The enzyme binds to its substrate, forming an enzyme-substrate complex
The reaction catalyzed by each enzyme is
very specific
is the region on the enzyme
where the substrate binds
The active site
of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction
Induced fit
in the Enzyme’s Active Site
In an enzymatic reaction, the substrate binds to the active site of the enzyme
The active site can lower an EA barrier by
Orienting substrates correctly
Straining substrate bonds
Providing a favorable microenvironment
Catalysis
Each enzyme has an optimal temperature in which it can function
Each enzyme has an optimal pH in which it can function
Optimal conditions favor the most active shape for the enzyme molecule
Cofactors are nonprotein enzyme helpers Cofactors may be inorganic (such as a metal in ionic form) or organic An organic cofactor is called a coenzyme Coenzymes include vitamins Enzyme Inhibitors
Competitive inhibitors bind to the active site
of an enzyme, competing with the substrate
Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective
Examples of inhibitors include toxins, poisons, pesticides, and antibiotics
The Evolution of Enzymes
Enzymes are proteins encoded by genes
Changes (mutations) in genes lead to changes
in amino acid composition of an enzyme
Altered amino acids in enzymes may result in novel enzyme activity or altered substrate specificity
Under new environmental conditions a novel
form of an enzyme might be favored
For example, six amino acid changes improved substrate binding and breakdown in E. coli
Chemical chaos would result if a cell’s metabolic pathways were not tightly regulated
A cell does this by switching on or off the genes that encode specific enzymes or by regulating
the activity of enzymes
Allosteric Regulation of Enzymes
Allosteric regulation may either inhibit or stimulate an enzyme’s activity
Allosteric regulation occurs when a regulatory molecule binds to a protein at one site and
affects the protein’s function at another site
Allosteric Activation and Inhibition
______________ is a form of allosteric regulation
that can amplify enzyme activity
One substrate molecule primes an enzyme to act on additional substrate molecules more readily
Cooperativity is allosteric because binding by a substrate to one active site affects catalysis in a different active site
Feedback Inhibition
Cooperativity
In feedback inhibition, the end product of a metabolic pathway shuts down the pathway
Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed
Figure 8.21
Localization of Enzymes Within the Cell
Structures within the cell help bring order to metabolic pathways
Some enzymes act as structural components
of membranes
In eukaryotic cells, some enzymes reside in specific organelles; for example, enzymes for cellular respiration are located in mitochondria
